JP2004363363A - Carrying apparatus, processing apparatus and carrying method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To highly accurately carry a cassette by performing spacing at the time of carrying the cassette, facilitating adjusting with less driving constituents thereof, and further enabling easily recognizing a grasping state or a positional relation of the flange of a cassette at the time of carrying the cassette. <P>SOLUTION: In the carrying apparatus 7 in which an arm 23 grasps a flange 19 provided on the top surface of an object 3 to be carried and carry the object 3, a plurality of sensors 0 are provided on the arm section 23, and the sensors recognize the presence or absence of the flange portion 19 in the arm 23 and a holding state. This arm section 23 is formed to be a cross section of U shape, optical sensors are provided on both ends of a side surface of the arm 23, and an optical sensor is provided on the center portion of the side surface thereof so that these optical sensors recognize the presence or absence of the flange 19 and the holding state. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a transfer apparatus, a processing apparatus, and a transfer method for transferring an object to be transferred, such as a closed storage container that stores a plurality of substrates such as semiconductor wafers.
[0002]
[Prior art]
As an example of a semiconductor manufacturing process, an object to be processed such as a semiconductor wafer (hereinafter, simply referred to as a wafer) is carried into a heat treatment apparatus, and a large number of wafers are formed at a time by a film formation process, an oxidation diffusion process, or a heat treatment such as a CVD process. Is performed. In this case, a loading / unloading stage provided in an apparatus for loading a cassette containing a plurality of wafers, a stocker for temporarily stocking the cassette, or a wafer stored in the cassette is transferred to a wafer. When the cassette is transferred to the wafer boat via the mounting machine, the cassette is transported to a predetermined position between holding stages for holding the cassette. The cassettes for accommodating the plurality of wafers include an open type open cassette and a FOUP (Front Opening Unified pod) cassette which is a closed type storage container.
[0003]
This FOUP cassette is provided so that the opening of the box body can be attached and detached by a lid so as to be sealed, and contains about 25 wafers inside. Since the FOUP cassette is a closed type, there is no risk that particles or the like around the cassette adhere to the wafer surface when transferring the wafer, and the cleanliness of the wafer surface is maintained. Therefore, the FOUP cassette is used as a wafer storage container. Cassettes tend to be used. The FOUP cassette is conveyed from the loading / unloading stage of the processing apparatus to the stocker or the holding stage, and is sequentially heat-treated, then stored in the FOUP cassette and conveyed to the next step.
[0004]
Conventionally, the following transport method has been known as a method for transporting this cassette. As one of the conventional methods, a FOUP transfer device driven by the cooperative movement of elevation, rotation, and horizontal movement is provided in the housing, and the bottom surface of the cassette placed on the stage is supported by the support arm of the FOUP transfer device. There is a method in which a cassette is transported to another stage while being supported (for example, see Patent Document 1). As another conventional method, a robot arm provided with a swivel table and an elevating mechanism is movably provided in a vertical direction and a horizontal direction, and a support plate rotatably supported by the robot arm has an opening larger than a flange of a cassette. It is transported by a transport robot having a structure in which a part is formed. At the time of this transfer, the cassette is lowered by lowering the support plate to insert the flange of the cassette through the opening, and then rotating the support plate to lock the flange to the support plate and raising the support plate to move the cassette to another position. This is a method of transporting to a stage (for example, see Patent Document 2).
[0005]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 2000-311935 [Patent Document 2]
JP-A-11-297786
[Problems to be solved by the invention]
However, the transfer method disclosed in Patent Document 1 is a method in which the cassette is transferred while the bottom surface of the cassette is supported by the support arm that is moved up and down, rotated, and horizontally moved. Not only is a space required to escape from the bottom surface, but also a FOUP transporter having a complicated articulated arm mechanism and the like is required. On the other hand, the transfer method of Patent Document 2 is a method in which the support plate is lowered by rotating the support plate in a state where the flange of the cassette is inserted through the opening and the flange is locked to the support plate. Therefore, since it becomes a combination mechanism of the plate rotation mechanism and the articulated arm mechanism, it becomes naturally a complicated mechanism. Neither Patent Document 1 nor Patent Document 2 has a safety mechanism such as a sensor for confirming a positional relationship when a cassette is delivered.
[0007]
The present invention has been developed in order to solve the above-mentioned problems, and an object of the present invention is to make it possible to efficiently use a space at the time of transporting a cassette, to reduce the number of driving elements, and to easily perform adjustment. In addition, the cassette can be transported with high precision by making it possible to easily confirm the gripping state and the positional relationship of the cassette flange when transporting the cassette.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, the invention according to claim 1 is a transporting device that grips and transports a flange portion provided on the upper surface of a transported object with an arm portion, and provides a plurality of sensors on the arm portion. This is a transport device that uses a sensor to recognize the presence or absence and the holding state of the flange portion in the arm portion.
[0009]
In the invention according to claim 2, the arm portion is formed to have a substantially U-shaped cross section, and first and third optical sensors are provided at both end portions of the side surface of the arm portion and a second optical sensor is provided at a central portion of the side surface, The transport device according to claim 1, wherein the presence / absence and the holding state of the flange portion are checked by these optical sensors.
[0010]
The invention according to claim 3 is the transport device according to claim 2, wherein the first and third optical sensors are transmission sensors, and the second optical sensor is a reflection sensor.
[0011]
The invention according to claim 4, wherein notches are formed at both side edges of the flange portion, and a protrusion is formed on an inward holding piece formed on both sides of a lower end of the arm portion. 4. The transfer device according to claim 1, wherein the positioning of the flange portion in the arm portion is performed by the protrusion and the protrusion.
[0012]
The invention according to claim 5 is the transfer device according to any one of claims 1 to 4, wherein the object to be transferred is a sealed cassette containing semiconductor wafers.
[0013]
According to a sixth aspect of the present invention, there is provided a mounting table for loading and unloading a transferred object provided with a flange portion on an upper surface, a storage shelf for storing the transferred object, and a processing object stored in the transferred object. In the processing apparatus provided with a holding table for transferring, the object to be transferred, which is located on the mounting table, the storage shelf or the holding table, is gripped by an arm portion with a flange portion provided on an upper surface of the transferred object. In addition, the present invention provides a processing apparatus provided with a transfer device in which a plurality of sensors are provided in the arm portion, and the presence / absence and holding state of the flange portion in the arm portion are recognized by the sensors.
[0014]
In the invention according to claim 7, the arm portion is formed to have a substantially U-shaped cross section, and first and third optical sensors are provided at both end portions of the side surface of the arm portion and a second optical sensor is provided at a central portion of the side surface. 7. The processing apparatus according to claim 6, wherein the presence / absence and the holding state of the flange portion are confirmed by these optical sensors.
[0015]
The invention according to claim 8 is the processing device according to claim 7, wherein the first and third optical sensors are transmission sensors, and the second optical sensor is a reflection sensor.
[0016]
The invention according to claim 9 is characterized in that notches are formed on both side edges of the flange portion, and a protrusion is formed on an inwardly-shaped holding piece formed on both sides of a lower end of the arm portion, and the notch portion is formed. 9. The processing apparatus according to claim 6, wherein the positioning of the flange portion in the arm portion is performed by the projection and the projection.
[0017]
According to a tenth aspect of the present invention, the positioning table, the storage shelf, and the holding table are provided with positioning pins for the transported body, and the lower surface of the transported body is fitted to the pins to be transported. 10. The processing apparatus according to claim 6, wherein a positioning groove for positioning the body is formed.
[0018]
The invention according to claim 11 is the processing apparatus according to any one of claims 6 to 10, wherein the object to be transferred is a sealed cassette containing semiconductor wafers.
[0019]
According to a twelfth aspect of the present invention, there is provided a transfer method in which a substantially U-shaped arm provided on a transfer mechanism grips and transfers a flange provided on an upper surface of a body to be transferred. And a holding state in which the flange portion is held by the arm portion by a plurality of sensors disposed on the arm portion.
[0020]
The invention according to claim 13 is a sensor for confirming an insertion state in which the arm section is inserted into the flange section, an insertion completed state, and a holding state in which the flange section is held by the arm section. 13. The transporting method according to claim 12, wherein the first and third optical sensors provided at the site and the second optical sensor provided at the center portion on the side face are used for checking.
[0021]
The invention according to claim 14 is the transport method according to claim 13, wherein the first and third optical sensors are transmission sensors, and the second optical sensor is a reflection sensor.
[0022]
The invention according to claim 15 is the processing method according to any one of claims 12 to 14, wherein the object to be transferred is a sealed cassette containing semiconductor wafers.
[0023]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of a transport device, a processing device, and a transport method according to the present invention will be described with reference to the drawings.
FIG. 1 is a perspective explanatory view of a processing apparatus using a transport device according to the present invention, and FIG. 2 is an enlarged explanatory view showing a transport device portion in FIG.
[0024]
The heat treatment apparatus shown in FIGS. 1 and 2 is an apparatus for carrying a semiconductor wafer W into a heat treatment apparatus and subjecting a large number of wafers W to a heat treatment such as a film formation process, an oxidation diffusion process, or a CVD process. In FIG. 1, a loading table 4 on which a sealed storage container (FOUP cassette) 3 as a transported object is placed is arranged on a loading / unloading stage 2 provided on a front surface of an apparatus main body 1 composed of a housing. A storage shelf 5 for temporarily storing the closed storage container 3 as a stocker and a holding table 6 for transferring the wafer W from the storage container 3 into the heat treatment area are arranged, and the mounting table 4, the storage shelf 5, and the holding table are arranged. The transfer of the storage container 3 to and from the storage container 6 is performed by a cassette transfer mechanism 7 which is a transfer device described later. The transfer of the closed storage container 3 is not limited to the above example, and includes, for example, the transfer between the mounting table 4 and the holding table 6, and these transfer steps are optional depending on the implementation. It is.
[0025]
Referring to FIG. 1, a closed storage container 3 held by a holding table 6 for transferring a wafer W into a heat treatment area has an opening 8 opened on the front surface of the container 3 hermetically covered with a lid 9. In a state in which the flange 10 is brought into contact with the wall 11 of the apparatus main body 1, the lid 9 in the locked state is removed by an unlocking mechanism (not shown), and the gate 12 provided on the wall 11 is actuated. The formed opening window 13 is opened, the wafer W is transferred from the opening window 13 to the wafer boat 15 by the wafer transfer mechanism 14, and then the wafer boat 15 is loaded into the heat treatment furnace 16 by an elevator (not shown). Thereafter, a predetermined heat treatment step is performed. After the processing is completed, the wafer boat 15 is unloaded from the heat treatment furnace 16 and, conversely, the wafer boat 15 is transferred by the wafer transfer mechanism 14 to the closed storage container 3 which is located on the holding table 6 and is open. The container 3 is transported by the cassette transport mechanism 7 from the loading / unloading stage 2 to the next step.
[0026]
The hermetically sealed storage container 3, which is the object to be transferred, can store about 25 wafers W in the container 3, is made of plastic, has a box shape, and has a weight of about 12 kg in a wafer storage state. I have. A rectangular neck 18 is formed on the upper surface of the container 3, and a rectangular flange 19 is provided at the upper end of the neck 18. are doing. Further, a plurality of positioning grooves 21 are formed on the lower surface of the container 3, and positioning pins 22 corresponding to the positioning grooves 21 are erected on the mounting table 4, the storage shelf 5 and the holding table 6, respectively. When the storage container 3 is placed on the table 4, the storage shelf 5, and the holding table 6, the storage container 3 is provided so as to be positioned at a predetermined position.
[0027]
The above-described cassette transport mechanism 7 includes a Z-axis elevating / lowering portion 7a, an X-axis horizontal portion 7b, and an articulated arm 7c, and an arm 23 having a substantially U-shaped cross section is provided at the tip of the articulated arm 7c. An inward holding piece 24 is formed on both sides of the lower end of the arm 23, and the flange 19 is held by the holding piece 24. The holding piece 24 may have a structure formed to protrude in a claw state. Further, in a state where the notch 20 formed in the flange portion 19 and the protrusion 25 formed in the holding piece 24 coincide with each other in a state where the arm portion 23 is gripped by the flange portion 19, it is confirmed that the position where the notch 20 formed in the holding portion 24 coincides is pierced. It is confirmed that the center of the arm portion 23 and the center of the flange portion 19 coincide with each other when viewed from the holes 26, 26. Further, when the projection 25 is locked in the notch portion 20, the notch portion The positioning of the flange portion 19 in the arm portion 23 is performed by the projection 20 and the projection portion 25, and the cassette can be transported in a stable state.
[0028]
3 and 4, a first transmissive optical sensor 28, a third transmissive optical sensor 29, and a center of the side surface are provided in a frame portion 27, which is both side portions of the arm portion 23 having a substantially U-shaped cross section. A reflection type second optical sensor 30 is provided at the position, the presence or absence of the flange portion 19 is confirmed by the transmission type optical sensors 28 and 29, and the reflection type optical sensor 30 is used to detect the flange of the closed storage container (cassette) 3. The state where the part 19 is held by the holding piece 24 of the arm part 23 is checked. The optical sensors 28, 29, and 30 in this example use photoelectric switches with built-in amplifiers. The transmission optical sensors of the photoelectric switches 28 and 29 include light-emitting sensors 28a and 29a and light-receiving sensors 28b and 29b. Are each constituted by a pair. In the frame 27, four safety mechanisms 31 each composed of a limit switch are provided in each corner so that the operation state is locked and stopped when an obstacle or the like is carelessly contacted. I have.
[0029]
5 and 6 are explanatory diagrams illustrating the relationship between the optical sensor provided on the arm 23 and the flange. In FIG. 5, when the flange portion 19 is inserted into the arm portion 23, light from the first and third sensors 28a and 29a on the light emitting side is blocked by the side surface of the flange portion 19 and turned ON. The second reflection type optical sensor (photoelectric switch) 30 cannot receive the reflected light at the detection distance L ′ (44 mm in this example) in FIG. 5 and at the detection distance L (26 mm in this example) in FIG. Since the detection distance is set to be such that the reflected light can be received, in the state shown in FIG. 5, the optical sensor 30 projects light to the surface of the neck portion 18 of the flange portion 19, so that light cannot be received at the detection distance L ', and the light sensor 30 is turned off. It becomes. In this state, as shown in FIG. 6, when the arm portion 23 is handed up in the Z-axis direction and the lower surface of the flange portion 19 is gripped by the holding piece 24, the first and third sensors 28a on the light emitting side, The light 29a is received by the light receiving side sensors 28b and 29b and turned off (or ON), and the second reflection type optical sensor 30 is reflected by the side of the flange portion 19 and can be detected. Since it is L, it is received and turned ON. It should be noted that the detection distance of the reflection type optical sensor 30 can be appropriately set according to the implementation.
[0030]
Next, the operation of the above embodiment will be described.
When the closed storage container (cassette) 3 located on the mounting table 4 in the state of FIG. 1 is transported by the cassette transport mechanism 7, the cassette transport mechanism 7 is composed of a Z-axis elevating unit 7a and an X-axis horizontal unit 7b. The X-axis, the Y-axis, and the Z-axis are moved by operating the joint arm 7c, and the arm 23 is positioned on the side of the flange 19 as shown in FIG. In this case, the optical sensors 28, 29, 30 are in the OFF state. Next, as shown in FIG. 8, when the X-axis horizontal portion 7b is operated to insert the arm portion 23 into the flange portion 19, the optical sensor 28 is turned on, and the optical sensors 29 and 30 are turned off. Further, as shown in FIG. 9, when the X-axis horizontal portion 7b is operated to insert the arm portion 23 into the flange portion 19 to the completion state, the optical sensors 28 and 29 are turned on, and the optical sensor 30 is in the off state. .
[0031]
Next, as shown in FIG. 10, when the arm 23 was raised in the Z-axis direction and the lower surface of the flange 19 was gripped by the holding piece 24, the reflection type optical sensor 30 reflected on the side of the flange 19. The reflected light is received and turned ON, and the sensors 28 and 29 are received by the light receiving side sensors 28b and 29b and turned OFF (or ON). Thereafter, as shown in FIG. 2, the cassette 3 is gripped by the arm 23 of the cassette transport mechanism 7 and transported to a predetermined transport position.
[0032]
In the embodiment described above, the transmission type first optical sensor 28, the transmission type third optical sensor 29, and the reflection type second optical sensor 30 are provided on the arm 23, and the transmission type optical sensor 28, At 29, the presence or absence of the flange portion 19 is confirmed, and at the reflection type optical sensor 30, the state of holding the flange portion 19 of the closed storage container 3 by the holding piece 24 of the arm portion 23 is confirmed. The transmission optical sensor (photoelectric switch) 30 ′ may be used as the transmission sensor 30 ′. This case will be described with reference to FIGS. 7 to 10. In FIG. 7, the optical sensors 28, 29, and 30 'are in the OFF state, and then, as shown in FIG. When 23 is inserted into the flange 19, the optical sensor 28 is turned on, and the optical sensors 29 and 30 'are turned off. Further, as shown in FIG. 9, when the X-axis horizontal portion 7b is operated and the arm portion 23 is inserted into the flange portion 19 to the completion state, the optical sensors 28 and 29 are turned ON, and the optical sensor 30 'is turned ON (or OFF) state. In this case, if the light projecting portion of the neck portion 18 of the flange portion 19 has a hollow structure, the light of the optical sensor 30 is received by the sensor on the light receiving side and is turned off. Next, as shown in FIG. 10, when the arm 23 is handed up in the Z-axis direction and the lower surface of the flange 19 is gripped by the holding piece 24, the transmission type optical sensor 30 ′ is placed on the side of the flange 19. The sensors 28 and 29 are turned on after being shielded from light, and are turned off by being received by the light-receiving sensors 28b and 29b.
[0033]
FIG. 12 shows another embodiment of the arm portion 32 provided in the cassette transport mechanism. The arm portion 32 having a substantially U-shaped cross section has a structure which expands and contracts in the horizontal direction. As shown in (a), it is positioned above the flange portion 19 of the cassette 3, and then, as shown in FIG. 3 (b), the arm 32 is driven so as to expand in the horizontal direction. As shown in (c), the arm 32 is moved horizontally so as to be reduced, and the arm 32 is further raised to be held by the holding piece 33 of the arm 32. In this case, the same optical sensors 28, 29, and 30 as those in the above-described embodiments are arranged on the side of the arm 32. In this case, the same operation and effect as described above are provided, and therefore, the description thereof is omitted.
[0034]
【The invention's effect】
As is clear from the above, according to the present invention, the flange is provided on the upper surface of the object to be transferred (closed container) and the container is held and transferred, so that the space during transfer is made more efficient. In addition, the positional relationship between the flange portions on the upper surface of the transported object located in the arm portion can be easily detected.
[0035]
ADVANTAGE OF THE INVENTION According to this invention, since the arm part of a substantially U-shaped cross section is inserted in the flange part of a to-be-conveyed body, and the optical sensor was provided in the arm part, there are few drive elements and adjustment can be performed reliably and easily. be able to. Further, the flange portion is securely held in the arm portion, and the transferred object can be transferred with high accuracy.
[0036]
In addition, when the transfer mechanism is disposed in the processing apparatus, it is possible to provide a processing apparatus in which space can be efficiently used and the number of driving elements is reduced, and the transfer apparatus can be transferred to the loading / unloading stage of the processing apparatus. When the body is placed, positioning is performed reliably, and high-precision transport is possible.
[0037]
Furthermore, it is possible to provide a transport method that achieves space efficiency at the time of transport, has few drive elements, is easy to adjust, and can reliably and easily detect the transport during transport of the transported object.
[Brief description of the drawings]
FIG. 1 is an explanatory perspective view of a processing apparatus using a transport device according to the present invention.
FIG. 2 is an enlarged explanatory view showing a transport device in FIG. 1;
FIG. 3 is an explanatory plan view showing a state in which a flange portion is gripped by an arm portion of the transfer device according to the present invention.
FIG. 4 is an explanatory front view of FIG. 3;
FIG. 5 is an explanatory front view illustrating a relationship between an optical sensor provided on an arm and a flange according to the present invention.
FIG. 6 is an explanatory front view showing a state in which a flange is held by an arm in FIG. 5;
FIG. 7 is an explanatory diagram showing a state before an arm portion is inserted into a flange portion in the present invention.
FIG. 8 is an explanatory view showing a state in which the arm shown in FIG. 7 is being inserted into the flange.
FIG. 9 is an explanatory view showing a state in which the arm portion of FIG. 8 has been completely inserted into the flange portion.
10 is an explanatory view showing a state in which the arm portion of FIG. 9 holds the cassette while holding the flange portion. FIG. 11 is a bottom view showing the object to be conveyed in the present invention.
FIGS. 12A, 12B, and 12C are explanatory views showing another example of a state in which the flange portion is gripped by the arm portion of the transfer device according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Apparatus main body 2 Loading / unloading stage 3 Sealed storage container (conveyed object)
4 mounting table 5 storage shelf 6 holding table 7 cassette transport mechanism (transport device)
18 Neck 19 Flange 20 Notch 23, 32 Arm 24, 33 Holding piece 25 Projection 28 First optical sensor 29 Third optical sensor 30 Second optical sensor

Claims (15)

In a transfer device for holding and transporting a flange portion provided on an upper surface of an object to be transported while gripping the arm portion with an arm portion, a plurality of sensors are provided on the arm portion, and the presence / absence and holding state of the flange portion in the arm portion are recognized by the sensors. A transport device characterized in that: The arm portion is formed in a substantially U-shaped cross section, and first and third optical sensors are provided at both end portions of the side surface of the arm portion and a second optical sensor is provided at a central portion of the side surface. The transfer device according to claim 1, wherein the presence or absence and the holding state are checked. The transport device according to claim 2, wherein the first and third optical sensors are transmission sensors, and the second optical sensor is a reflection sensor. Notches are formed at both side edges of the flange portion, while projections are formed on holding pieces formed inward on both sides of the lower end of the arm portion, and the notch and the projection form an inside of the arm portion. The transport device according to claim 1, wherein the positioning of the flange portion is performed. 5. The transfer device according to claim 1, wherein the transfer target is a sealed cassette containing semiconductor wafers. A mounting table for loading and unloading a transferred object provided with a flange portion on the upper surface, a storage shelf for storing the transferred object, and a holding table for transferring the processed object stored in the transferred object. In the processing apparatus provided, the transported object located on the mounting table, the storage shelf or the holding table is gripped by an arm portion with a flange portion provided on the upper surface of the transported object, and a plurality of A transfer device provided with a sensor for detecting the presence or absence and the holding state of the flange portion in the arm portion using the sensor. The arm portion is formed in a substantially U-shaped cross section, and first and third optical sensors are provided at both end portions of the side surface of the arm portion, and a second optical sensor is provided at a central portion of the side surface. 7. The processing apparatus according to claim 6, wherein the presence / absence and the holding state of the copy are confirmed. The processing apparatus according to claim 7, wherein the first and third optical sensors are transmission sensors, and the second optical sensor is a reflection sensor. Notches are formed at both side edges of the flange portion, while projections are formed on holding pieces formed inward on both sides of the lower end of the arm portion, and the notch and the projection form an inside of the arm portion. 9. The processing apparatus according to claim 6, wherein the positioning of the flange portion is performed. The positioning table, the storage shelf, and the holding table are provided with the positioning pins for the transported object, and the lower surface of the transported object is formed with positioning grooves for fitting the pins and positioning the transported object. The processing apparatus according to claim 6, wherein the processing is performed. The processing apparatus according to any one of claims 6 to 10, wherein the object to be transported is a sealed cassette containing semiconductor wafers. A transport method in which a substantially U-shaped arm provided in a transport mechanism grips and transports a flange provided on an upper surface of a body to be transported, wherein the arm is inserted into the flange and insertion is completed. A transfer method, wherein a state and a holding state in which the flange section is held by the arm section are confirmed by a plurality of sensors provided in the arm section. Sensors for confirming the insertion state in which the arm part is inserted into the flange part, the insertion completed state, and the holding state in which the flange part is held by the arm part are provided at first and second end portions on both side surfaces of the arm part. 13. The transport method according to claim 12, wherein the confirmation is performed by one of the three optical sensors and a second optical sensor provided at a central portion of the side surface. 14. The transport method according to claim 13, wherein the first and third optical sensors are transmission sensors, and the second optical sensor is a reflection sensor. 15. The processing method according to claim 12, wherein the object to be transported is a sealed cassette containing semiconductor wafers.

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